1. Field of the Invention
This invention relates to a so-called non-magnetic contacting one component-type development system which comprises supplying a non-magnetic toner to a development roller via a sub-roller and contacting the toner supplied to the development roller with the surface of a photosensitive drum on which an electrostatic latent image is formed to perform development of the electrostatic latent image.
2. Description of the Prior Art
In the formation of an image in an electrophotographic method, an electrostatic latent image is formed in a photosensitive drum, the electrostatic latent image is developed with a toner to form a visual image, the toner image is transferred to a transfer paper, and then fixing this image.
The development methods used in this electrophotography include a two-component type magnetic development method using a mixture of a toner and a magnetic carrier, a one component type magnetic development method using a one component type toner containing a magnetic powder, and a non-magnetic contacting one component type development method using a non-magnetic one component-type toner. In view of the cost of a developer, the miniaturization and cost of a development machine, and the simplicity of the operation, the non-magnetic contacting one component type development method is the best.
The desire to super-miniaturize an apparatus for non-magnetic contacting one component type developing system is great, and in order to meet this requirement, the photosensitive drum together with the development roller and the toner-supplying sub-roller should be miniaturized, and these machines should be contacted with each other. For this purpose, the driving motor and the driving power source should naturally be miniaturized. Rotating directions of the devlopment roller and the sub-roller and rotating directions of the development roller and the photosensitive drum should be prescribed so that the driving torques will be decreased.
Japanese Laid-Open Patent Publication No. 197710/1997 discloses a development apparatus comprising a latent image-forming member (photosensitive drum), a toner layer-carrier (development roller) which carries the toner layer on the surface and develops the latent image formed on the latent image-forming member by press-contacting with the above latent image-forming member and rotating, a toner supplying member (sub-roller) for supplying the toner to this toner layer-carrier, and a supplying auxiliary member contacting the supplying member, or arranged in the vicinity of the toner suppying member. This Patent Publication also describes a method of development by using a non-magnetic one component toner which is obtained by a pulverization and has an average circularity degree (C) of not larger than 0.94. The average circularity degree (C) is calculated by the following formula: EQU C=A/AL
wherein A is the area of the projected image of the toner, and AL is the area of a circle having the same circumferential length as that of the toner projected image.
However, when an irregularly shaped non-magnetic one component-type toner obtained by this pulverization method is applied to the above super-miniaturized non-magnetic contacting one component-type development system, at the time of supplying the toner from the sub-roller to the development roller, a part of the toner not supplied to the development roller tends to collect successively in the bottom of the development housing. In such a super-miniaturized development unit, the space between the bottom of the development housing and the sub-roller is very narrow, and the collected toner reaches a nipping position between the development roll and the sub-roller. For this reason, the torque (to be referred to as a development torque) becomes very large, and finally the driving gear becomes locked.
In the non-magnetic contacting one component-type development system, the thickness of the layer of the one component-type toner supplied to the development roller is made thin by a blade (toner thin layer forming blade), and the development is carried out by contacting this thin toner layer with the photosensitive drum. As this blade, a metallic conductor such as SUS is used in order to apply voltage to impart a charge to the toner.
However, when development is carried out by using the toner thin layer forming blade composed of such a metallic conductor, as the development is repeated, the toner adheres to the blade. A thin layer of the toner is not formed on a portion of the development roller corresponding to the blade portion to which the toner adheres, and black striae or white striae occur in the resulting image. This tendency is especially marked when the development is carried out at a high temperature and under high humidity. When the development apparatus or a toner obtained by the pulverization method is used, it is impossible to settle this problem.